Conventionally, sewing machines that enable skipping a stitch during the sewing work have been widely known. An example of those sewing machines can be found in the patented document 1. The sewing machine according to the patented document 1 has the following structure.
The sewing machine includes a needle bar, having an engaging member (engaging device) provided at an upper portion thereof and disposed so as to vertically reciprocate with respect to a head frame; and a carriage set to be driven by a main shaft and to vertically reciprocate parallel to the needle bar; and the carriage is provided with a latching element (latching portion) which is set to move between an engaging position where the latching element can be engaged with the engaging member and a retreated position where the latching element is not engaged therewith, and which is constantly subjected to a biasing force applied in a direction toward the engaging position from the retreated position, so that the latching element normally remains engaged with the engaging member of the needle bar, to thereby cause the needle bar to vertically reciprocate with the vertical reciprocating motion of the carriage.
The sewing machine also includes an operating mechanism (skipping mechanism) including a solenoid with a rotating shaft set to reciprocatively rotate and to be driven in one direction when power is supplied to the solenoid; and an engaging portion (operating member) radially spaced from the rotating shaft of the solenoid and connected to the rotating shaft of the solenoid, so as to circumferentially rotate with the rotation of the rotating shaft of the solenoid; and the engaging portion is engaged with the latching element provided on the carriage when power is supplied to the solenoid, to thereby allow the latching element to recede from the engaging position to the retreated position, and allows the latching element, when power to the solenoid is disconnected, to return to the engaging position because of biasing force applied by a spring provided inside the solenoid.
With the sewing machine thus constructed according to the patented document 1, when the carriage vertically reciprocates with the latching element of the carriage being located at the position for engagement with the engaging member of the needle bar, the needle bar is made to vertically reciprocate together with the carriage, to thereby perform the sewing work.
For skipping a stitch during such sewing work, power is supplied to the solenoid in the operating mechanism to rotate the engaging portion, thereby driving the latching element to the retreated position where the latching element is not engaged with the engaging member of the needle bar. Under such state, the vertical reciprocating motion of the carriage is not transmitted to the needle bar, and hence the stitch is skipped.
On the other hand, for returning to the normal sewing mode from the stitch-skipping mode, power to the solenoid in the operating mechanism is disconnected, so that the engaging portion rotates toward the engaging position and the latching element returns to the engaging position, and therefore the needle bar is made to vertically reciprocate with the vertical reciprocating motion of the carriage, so as to perform the normal sewing work.
Further, the sewing machines known in the art that allow skipping a stitch during the sewing work include the one disclosed in the patented document 2. The sewing machine according to the patented document 2 has the following structure.
The sewing machine includes a needle bar disposed so as to vertically reciprocate with respect to a fixed block (frame) of a machine head but constantly biased upward, and having an engaging member (engaging device) provided at an upper portion of the needle bar; a pressing roller (positioning block) of a needle bar stopper that defines an upper dead point of the needle bar; and a carriage and a lock element mounting base (carriage) set to be driven by an upper shaft (main shaft) so as to vertically reciprocate parallel to the needle bar; and the carriage is provided with a lock element (latching portion) which is set to move between an engaging position where the lock element can be engaged with the engaging member and a retreated position where the lock element is not engaged therewith, and which is constantly subjected to a biasing force applied in one direction so as to return from the retreated position to the engaging position, so that the lock element normally remains engaged with the engaging member of the needle bar, to thereby cause the needle bar to vertically reciprocate with the vertical reciprocating motion of the carriage.
Further, the lock element is made to swing by a driving mechanism (skipping mechanism) between the engaging position and the retreated position.
With the sewing machine thus constructed according to the patented document 2, when the lock element of the carriage is at the position for engagement with the engaging member of the needle bar, the needle bar is made to vertically reciprocate with the carriage, to thereby perform the sewing work.
For skipping a stitch during such sewing work, the driving mechanism causes the lock element to the retreated position so as to disengage the lock element from the engaging member of the needle bar thus allowing only the carriage to vertically reciprocate, and hence the stitch is skipped.
For returning to the normal sewing mode from the stitch-skipping mode, the driving mechanism causes the lock element to return to the engaging position thereby allowing the needle bar to vertically reciprocate with the vertical reciprocating motion of the carriage, so that the normal sewing work can be performed.
When the lock element is disengaged from the engaging member of the needle bar by moving to the retreated position in the stitch-skipping process, the upward motion of the needle bar caused by inertia can be delimited at the position corresponding to the upper dead point by the pressing roller of the needle bar stopper.
It is to be noted that the terms in the parenthesis accompanying some terms employed in the description of the patented documents 1, 2 correspond to the constituents according to the present invention having the same or equivalent function, nature, means or feature to those of the patented documents 1, 2.
[Patented document 1] Japanese Patent No. 2866488
[Patented document 2] Japanese Unexamined Patent Publication No. 2002-66183
In order to increase the speed of the vertical reciprocating motion of the needle bar (for example, 10 to 20% faster) in the sewing work including the stitch-skipping, it is necessary to cause the latching element and the engaging member of the needle bar to get mutually engaged and disengaged quicker, according to the increase in vertically reciprocating speed of the needle bar.
In the case of the sewing machine according to the patented document 1, it might be a solution to employ a larger solenoid to obtain greater driving force, to thereby cause the latching element to be more quickly disengaged from the engaging member of the needle bar. Employing a larger solenoid leads, however, to an increase in cost and is hence not advantageous.
On the other hand, to cause the latching element to return more quickly to the engaging position with the engaging member of the needle bar, it might be an option to increase the spring force of the spring inside the solenoid to thereby eliminate obstruction against the latching element returning to the engaging position with its own biasing force. However, increasing the spring force of the spring inside the solenoid inversely creates resistance against the driving force of the solenoid driving the latching element to be disengaged from the engaging member of the needle bar, thus decreasing the disengaging speed of the latching element from the engaging member of the needle bar.
Methods of causing the latching element to return more quickly to the engaging position with the engaging member of the needle bar also include increasing the spring force biasing the latching element toward the engaging position. Increasing the biasing force creates, however, greater force resisting against the driving force of the solenoid causing the latching element to be disengaged from the engaging member of the needle bar, thus leading to the disadvantage that the latching element gets disengaged from the engaging member of the needle bar at reduced speed.
Consequently, as described above, the conventional sewing machine according to the patented document 1 has the drawback that the increase in vertically reciprocating speed of the needle bar cannot be achieved, because it is impossible to increase the engaging speed nor the disengaging speed between the latching element and the engaging member of the needle bar according to the increase in vertically reciprocating speed of the needle bar.
Also, for skipping the stitch during the normal sewing work with the sewing machine according to the patented document 2, the lock element is moved to the retreated position while the carriage is moving toward the upper dead point with the needle bar, and the needle bar released from the engagement with the lock element keeps ascending at the same pace thus to collide with the pressing roller of the needle bar stopper, and the needle bar, upon once descending because of the reaction of the collision, is again driven to ascend with great force by the upward biasing force, halfway of the descending motion. Then the needle bar again collides with the pressing roller thus to be caused to descend by the reaction, but is driven upward again by the biasing force. Thus, the needle bar repeats the descending and ascending motions in the vicinity of the upper dead point, which creates the drawback that the position of the needle bar is not stabilized immediately upon reaching the upper dead point.
Since the needle bar repeats the vertical reciprocating motion even after reaching the upper dead point, and is hence not stably set at the position corresponding to the upper dead point, the lock element of the carriage cannot be accurately engaged with the engaging member of the needle bar even though the carriage ascends again after descending to thereby have the lock element get engaged with the engaging member of the needle bar at the position corresponding to the upper dead point, because the timing is too short before the needle bar starts to descend after reaching the upper dead point, and therefore only the carriage descends without being accompanied with the needle bar, which leads to failure in performing the sewing work as designed, and to create a defective embroidery pattern.